1. Field of Invention
The present invention relates generally to optical fibers with side emissive properties. More particularly, the examples disclosed herein are directed to optical fibers having Surface Light Field Emulation (s-LiFE) properties (herein after “s-LiFE optical fibers”), systems using them and method of making the same. The s-LiFE optical fibers are used for displays or general illuminations and to be produced at a low cost.
2. Discussion of Related Art
Optical fibers are used primarily in the telecommunication industry. An optical fiber typically comprises a core and cladding. The cladding usually has a slightly lower refractive index than that of the core. Light typically strictly propagates within the optical fiber core through total internal reflection and does not leak out if there are no defects or impurities in the material and structure.
Although most optical fibers have been manufactured to meet telecommunication requirements, i.e. to achieve essentially no light leaking out, i.e. side emission, through its propagation pathway, some side-emitting optical fibers have also made as a component in an illumination system. These side-emitting optical fibers are made by employing modification techniques to encourage the light to exit the optical fiber through its length.
U.S. Pat. No. 7,137,416 teaches a method that includes weaving optical fibers as warps or weft threads into a piece of fabric. In another words, the optical fibers are subjected to some degree of bending (generally known as “micro-bending”) in the fabric to give out light. U.S. Pat. Nos. 6,206,533 and 4,234,907 teach a surface damaging technique applying a single scratch or notch at intervals along the optical fiber length. French Pat. No. 2,626,381 explored the extreme of removing part of the optical fiber cladding layer in order to emit light.
U.S. Pat. No. 7,433,565 teaches addition of diffuser particles to the core. The diffuser particles are distributed to scatter light being transmitted along the core so that some of the scattered light exits the sides of the optical fiber. U.S. Pat. No. 5,631,994 also disclosed the technique of using fluorescent dopants in the optical fibers to achieve side emitting.
The micro-bending, surface damaging techniques and using diffuser particles and fluorescent dyes can only achieve uncontrolled and interrupted emission through the optical fiber length.
U.S. Pat. No. 5,631,994 teaches a light extraction overlay which is formed from an optically transparent substrate, fabricated by conventional manufacturing processes, such as a molding process. An adhesive backing is applied to the overlay so that it can adhere to the fiber core. The process itself requires some precision to achieve the intended property. More importantly, the overlay creates two extra interfaces, the fiber/adhesive interface and the adhesive/substrate interface. The additional interfaces will cause undesirable scattering or reflection.
U.S. Pat. No. 7,213,947 teaches a technique using a reflector to modify the interface between the core and the cladding so that the light striking the interface between the cladding and the core may be transmitted out through the cladding, rather than reflected back into the core, appearing as illumination. The reflector is carefully engineered and in the size of micrometers.
The light extraction overlay and reflector technique are able to achieve carefully engineered emission but the processes are complicated.
Our Surface Light Field Emulation (s-LiFE) optical fiber disclosed herein allows the light to come out in a more controlled fashion, which offers significant design flexibility for designers to tailor emission position, intensity and color for different applications. The present invention can be used to scientifically engineer light emitting from an optical fiber by combining and balancing light scattering, refraction, reflection and filtering to realize individual visual effects. Designers can choose to make the emission appearance to look more like a diamond or precious metals such as silver or gold, or some combination as they prefer.
In addition, the present invention uses dimensions in the nanometers range, which offers minimal intrusion to the physical structure of the optical fiber. The current invention is much smaller in dimension compared to the above-mentioned inventions. Structure deformation caused by micro-bending is in the size of micrometers and reflectors in the optical fiber are often in micrometer to millimeter range. The bigger the size of deformations, the more the physical strength and mechanical flexibility of the optical fiber is compromised. The present invention uses structure intrusions ten to hundred times smaller, thus providing better structural integrity of the optical fiber. Given the advantages, the present invention has broader applications, more flexibility and better adaptability in incorporating into various illumination systems.